Aging is the consequence of the loss of functionality and the loss of resistance or adaptability to stress. Free radicals have been shown to play important roles in the basic aging process. Over-expression of superoxide dismutase and catalase has been shown to increase the mean and maximum life span (about 30%) of Drosophila. Dietary restriction, which protects against oxidative damage, also retards the aging process in rodents. Free radicals have also been implicated in life-shortening and age-associated disorders such as Alzheimer's disease, Parkinson's disease and atherosclerosis. To study the molecular mechanisms that mediate the effect of free radicals, we have developed a free radical-resistant cell line (PC12-MR) by mimicking the chronic exposure to free radicals in the process of aging. Since PC 12-MR cells are resistant to superoxide, the expression of some genes must be altered to protect cells from free radical damage. The possible candidate genes may include anti-oxidant enzymes (e.g., superoxide dismutase, catalase, and glutathione peroxidase) and cell death inhibitors (e.g., Bcl-2 and Bcl-XL). Our preliminary studies have also found that the level of cGMP in PC 12-MR cells is elevated. It is possible that cGMP may play a protective role against oxidative stress. Since mammalian cells may have developed multiple systems to protect against environmental and endogenous oxidative stress during evolution, it is possible that the expression of other novel genes is also altered in PC 12-MR cells to render them resistant to free radicals. To examine these possibilities, we propose: l) to examine whether the expression of genes known to be involved in scavenging free radicals and in inhibiting apoptosis are altered in PC 12-MR cells, and whether these identified genes contribute to the protection of PC 12-MR cells from free radical insult; 2) to examine whether membrane-bound guanylate cyclase/cGMP exerts a protective effect against free radicals; and 3) to identify other novel genes that render PC12-MR cells resistant to free radical insult employing the differential display technique. The information generated from this study will help identify genes that can prevent cell death caused by free radicals. My long-term goal is to understand the molecular mechanisms of aging and particularly the mechanisms that protect cells from free radical insult, so that therapeutic intervention may be developed to delay aging process and be applied as well to age- associated diseases such as Alzheimer disease, Parkinson's disease and atherosclerosis.